There are a number of means to prepare such starting magnesium compounds. One way is disclosed in the article "Alkoxymagnesium Halides" by Turova et al, Journal of Organometallic Chemistry, 42, pages 9-17 (1972), which disclosure is herein incorporated by reference. The phase diagram shown in the attached FIG. 2 is taken from FIG. 1 of the Turova article. As mentioned above it is much preferred that the "R" and "R'" in the crystal structure be a methyl group. Accordingly, the remainder of the disclosure will reference methanol, methyl or methoxy groups.
One method to prepare the crystal structures of the present invention (as disclosed in Turova et al) involves preparing solutions of MgCl.sub.2 in methanol and Mg(OCH.sub.3).sub.2 in methanol, then mixing the controlled solutions in a mole ratio of MgCl.sub.2 to Mg(OCH.sub.3).sub.2 of 1:3 and then removing the methanol solvent until the crystals are formed. If desired, small amounts of vaseline oil may be added to improve crystallization.
Another equivalent method disclosed herein involves the use of Mg metal, MgCl.sub.2 and methanol. In this method three equivalents of the Mg is dissolved in a methanolic solution of MgCl.sub.2 to again provide the 3:1 mole ratio of methoxide to chloride.
The extremely narrow stability range required by the ternary phase relationship would tend to make either of the above methods difficult for commercial implementation. As discussed in the above-mentioned article by Turova, it requires great care to control solution concentrations and conditions to prepare stable crystal structures. Such care may be possible under laboratory conditions, but such level of care may be very difficult under commercial plant conditions. Accordingly, applicant has also discovered a method for preparing such structures by using a "buffer" technique. In this technique advantage is taken of the nearly equivalent ability of the Si-OCH.sub.3 and Si-Cl bonds to use SiCl.sub.4 to remove excess methoxide and virtually buffer the methanolic solution over a wide range of effective methoxide concentrations.